Bayonet primers have long been used in tank ammunition. Conventional bayonet primers have a cartridge case base that is ejected into the confines of the fighting vehicle after the propelling charge has been ignited by the primer. Unfortunately, in the case of originally designed bayonet type primers, the ejected case base, including the steel primer body created a hot metal tube that was able to come into contact with an ammunition round that was being held ready for loading after the chambered round was extracted. The ejected round could land on the next round and start a fire within the close confines of the fighting vehicle.
To promote safety for the crew of the fighting vehicle and solve the aforesaid fire hazard, tank ammunition primers were sealed with silicone rubber and other materials in order to keep them from igniting when contacting a hot ejected round. Unfortunately, such exterior rubber seals are expensive and have other significant drawbacks.
One current method of sealing bayonet primers uses a paper liner placed inside the flashtube. The flashtube is then dipped in a vat of lacquer, thereby filling flashholes with lacquer to protect the pyrotechnic charge from moisture. Excess lacquer must be scraped from the exterior of the flashtube. Finally, the lacquer plugs so formed are air dried. This is necessary because the various ignition charges are very hygroscopic and the presence of moisture will have an adverse effect upon the ignition charges, causing their degradation and possibly resulting in misfires.
As noted in U.S. Pat. No. 5,465,665 to Diehl issued Nov. 14, 1995, entitled "Primer," a typical bayonet type primer includes a primer head for housing an initial firing stage of a round. An ignition element, pressed into place in the confines of the primer head, is charged with a pyrotechnic composition that starts the firing train. When activated, the ignition element disperses a flame through a retainer. The flame sets off an explosive charge of black powder. The black powder charge in turn propagates through a closing plug, which acts as a directional device to a third charge of Benite. Benite is comprised mainly of nitrocellulose and black powder in a stranded form and other pyrotechnic formulations, housed in the primer body. The third charge propagates through holes in the metal primer body initially sealed with a lacquer. This charge, propagating through the primer body, ignites the propelling charge contained in the ammunition case moving the ammunition projectile such as a penetrator out of the gun barrel and to its target. U.S. Pat. No. 5,465,665 is incorporated in its entirety herein by reference. Unfortunately, Diehl proposes using a hollow tubular one-piece body comprised of a molded thermoplastic material that body still requires lacquer sealing. Alternatively, the perforations in the body may be molded such that there is a thin skin covering the perforations, but this latter method still requires sealing many individual flash holes.
There are several drawbacks to primers constructed in accordance with such known methods. One such drawback is inherent in the use of the sealing lacquer because the lacquer consistency varies within batches and between batches with respect to viscosity and percent solids. Such inconsistencies make the process variable and difficult to control.
Other drawbacks of conventional sealing by paper liner are caused by the method of applying the lacquer that can create bubbles in the flash holes. The presence of bubbles results in a marginal seal. The lacquer itself has undesirable moisture permeability. Further still, it is difficult to determine by inspection whether all flashholes are sealed.
Furthermore, a paper liner, if used, does not always seat tightly to the interior of the flashtube and lacquer may leak into the interior of the primer. As a further drawback, a paper liner is susceptible to being caught by charge strands of Benite during loading. Once so damaged, it is difficult to load the primer charge.
In other types of tank ammunition primers, much shorter primers were used. For example, a stub plastic liner was used with short primers of about one inch in length. Such stub liners were made by injection molding. Injection molded parts are not practical for liners suitable for use with longer bayonet primers. It has been found that injection molding is not desirable for longer liners because 1) the draft angle required to extract the part from the mold reduced the internal volume to the point that sufficient charge could not be loaded, and 2) the injection pressures required to fill the mold quickly pushed the mandrel core against the sidewall, thereby ruining the part.